Barnosky et al (2011) bring to the table evidence to suggest that currently, the Earth itself could be heading straight into a 6th mass extinction event, the previous 5 taking place over the last 540 millions years (a mass extinction event, as defined in the paper, is where the Earth loses over 75% of species over a geologically short time-period).
The previous 5 mass extinction events have taken place near the end of the Ordovician (about 443 Ma), Devonian (about 375 Ma), Permian (about 250 Ma), Triassic (about 200 Ma) and Cretaceous (about 65.5 Ma) periods. The Ordovician extinction event led to a loss of about 86% of species, the Devonian about 75% loss of species, the Permian about 96% loss of species, the Triassic about 80% of species and the Cretaceous loss of about 76% of species. All of these events are associated with climate change through global warming due to increasing levels of carbon dioxide, increasing levels of volcanism and ocean acidification apart from the Cretaceous extinction, where an asteroid impact caused dramatic global cooling.
The increase in species extinction has been heightened by human activity and increasing human biomass. Human activities such as habitat fragmentation, hunting, the spread of pathogens, changing global climate and the introduction of non-native species (alien species) has led to the decline of biodiversity. This article highlights that although these extinctions are taking place, if no action is done to mitigate the process by which the extinctions occur, then biodiversity levels will never recover.
Species introductions and invasions have been ever present leading to the extinction of native wildlife and has more often than caused a permanent change in ecological interactions that take place within that ecosystem. This can happen through the introduction of a new predator, such as the Nile Perch in Lake Victoria, or the removal of a trophic level from a food chain by over hunting. As stated by Clout and Williams (2009) there are three broad pathways along which alien species are introduced; natural spread, accidental introduction and deliberate introduction. Accidental and deliberate introductions have become the more dominant pathways through increased travel and trade and biological control of pests or of previous introduction.
An example of the natural spread of invasive species is the Queensland fruit fly, a native to South East Queensland (Clout and Williams, 2009). The extension of its natural habitat has been due to human activity changing the environment. The spread has now incorporated most of Eastern Australia and has become a severe pest in the agricultural industry for particular crops. It should be noted that the expansion also took place after the introduction of exotic fruits and vegetables to the natural range and therefore is a direct consequence of human activity, not an introduction of invasive species in its own right.
Accidental introductions have become more and more common with increasing travel and trade, as well as an expansion of the pet and horticultural industry. New Zealand, which is considered especially vulnerable to invasive alien species (Warren, 2001), was first 'invaded' by the Pacific rat around AD 50-150 (Veitch and Clout, 2001) when Polynesian visitors first visited the island. There is evidence to suggest that this rat alone caused the depletion/extinction of a many number of bird, lizard and insect species (Holdaway, 1989). Through European settlement, a combination of deliberate and accidental introductions of alien species has impacted the ecology of an island that has a long independent evolutionary history (Warren, 2001).
Deliberate introductions have been more prevalent in recent history for many reasons, including pasture and genotype improvement, new crops, biological control, horticulture, hunting, research and many others (Clout and Williams, 2009). Again, regarding New Zealand, when colonization first took place by European settlers in the early 1800's, they brought with them a wide range of species to make the new land more like the place they have just left. This lead to outbreaks of non-native population booms, which in turn led to further introductions as a form of biological control, a worsening spiral. Clout and Williams (2009) state that there are three main pathways within deliberate introduction; Biological control, plant introductions and smuggling. As seen with New Zealand, control of introductions and invasive movements needs to be controlled.
The current situation of species extinction has therefore been greatly enhanced by human activity. Although direct comparison of extinction rates with historic mass extinction events has many flaws, the rate of extinction presently are higher than expected and need to be addressed (Barnosky et al, 2011).
From here on in, this blog will address further species extinctions and the implications of invasive species and their role in this process, whether their introductions are natural, deliberate or accidental.
The previous 5 mass extinction events have taken place near the end of the Ordovician (about 443 Ma), Devonian (about 375 Ma), Permian (about 250 Ma), Triassic (about 200 Ma) and Cretaceous (about 65.5 Ma) periods. The Ordovician extinction event led to a loss of about 86% of species, the Devonian about 75% loss of species, the Permian about 96% loss of species, the Triassic about 80% of species and the Cretaceous loss of about 76% of species. All of these events are associated with climate change through global warming due to increasing levels of carbon dioxide, increasing levels of volcanism and ocean acidification apart from the Cretaceous extinction, where an asteroid impact caused dramatic global cooling.
The increase in species extinction has been heightened by human activity and increasing human biomass. Human activities such as habitat fragmentation, hunting, the spread of pathogens, changing global climate and the introduction of non-native species (alien species) has led to the decline of biodiversity. This article highlights that although these extinctions are taking place, if no action is done to mitigate the process by which the extinctions occur, then biodiversity levels will never recover.
Species introductions and invasions have been ever present leading to the extinction of native wildlife and has more often than caused a permanent change in ecological interactions that take place within that ecosystem. This can happen through the introduction of a new predator, such as the Nile Perch in Lake Victoria, or the removal of a trophic level from a food chain by over hunting. As stated by Clout and Williams (2009) there are three broad pathways along which alien species are introduced; natural spread, accidental introduction and deliberate introduction. Accidental and deliberate introductions have become the more dominant pathways through increased travel and trade and biological control of pests or of previous introduction.
An example of the natural spread of invasive species is the Queensland fruit fly, a native to South East Queensland (Clout and Williams, 2009). The extension of its natural habitat has been due to human activity changing the environment. The spread has now incorporated most of Eastern Australia and has become a severe pest in the agricultural industry for particular crops. It should be noted that the expansion also took place after the introduction of exotic fruits and vegetables to the natural range and therefore is a direct consequence of human activity, not an introduction of invasive species in its own right.
Accidental introductions have become more and more common with increasing travel and trade, as well as an expansion of the pet and horticultural industry. New Zealand, which is considered especially vulnerable to invasive alien species (Warren, 2001), was first 'invaded' by the Pacific rat around AD 50-150 (Veitch and Clout, 2001) when Polynesian visitors first visited the island. There is evidence to suggest that this rat alone caused the depletion/extinction of a many number of bird, lizard and insect species (Holdaway, 1989). Through European settlement, a combination of deliberate and accidental introductions of alien species has impacted the ecology of an island that has a long independent evolutionary history (Warren, 2001).
Deliberate introductions have been more prevalent in recent history for many reasons, including pasture and genotype improvement, new crops, biological control, horticulture, hunting, research and many others (Clout and Williams, 2009). Again, regarding New Zealand, when colonization first took place by European settlers in the early 1800's, they brought with them a wide range of species to make the new land more like the place they have just left. This lead to outbreaks of non-native population booms, which in turn led to further introductions as a form of biological control, a worsening spiral. Clout and Williams (2009) state that there are three main pathways within deliberate introduction; Biological control, plant introductions and smuggling. As seen with New Zealand, control of introductions and invasive movements needs to be controlled.
The current situation of species extinction has therefore been greatly enhanced by human activity. Although direct comparison of extinction rates with historic mass extinction events has many flaws, the rate of extinction presently are higher than expected and need to be addressed (Barnosky et al, 2011).
From here on in, this blog will address further species extinctions and the implications of invasive species and their role in this process, whether their introductions are natural, deliberate or accidental.
Interesting post. Of course, one of the main problems with comparing extinction rates is the quality of fossils that preserve. I think several of the earlier mass extinctions were based on marine organisms? In the current day, we know least about marine organisms, compared to e.g. terrestrial ones.
ReplyDeleteOn a technical point, when you use citation, hyperlink it to the journal page.